A relay technique is standardized in IEEE (Institute of Electrical and Electronics Engineers) 802.16j. Further, in 3GPP (3rd Generation Partnership Project) LTE-A (Long Term Evolution-Advanced) also, a technique using a relay node (RN) is studied actively in order to improve the throughput of a user equipment (UE) located at the cell edge.
The relay node receives a signal transmitted from a base station, amplifies the signal and transmits the amplified signal to the user equipment in the downlink. Such a relay in the relay node ensures a higher signal-to-noise ratio compared to directly transmitting a signal from the base station to the user equipment. Likewise, the relay node relays a signal transmitted from the user equipment to the base station in the uplink, thereby maintaining a high signal-to-noise ratio. The relay node is disclosed in the following non-patent literatures 1 to 3, for example.
The transmission power of a signal transmitted by the user equipment near the cell edge is sufficiently small. Thus if there is no relay node, interference with the adjacent cell is not a significant problem.